What is the normal function of the CLN3 gene?

The CLN3 gene provides instructions for making a protein that is found in the membranes of multiple cellular structures, but whose function is not completely understood. Researchers have proposed several potential functions for the CLN3 protein, including protein transport (trafficking), cell-to-cell communication, and the transmission of chemical signals. The CLN3 protein may also be involved in the organization of the cell's structural framework (cytoskeleton), movement of cell structures, and in the self-destruction of cells (apoptosis). Additionally, the CLN3 protein appears to be important for the normal function of cell structures call lysosomes. Lysosomes are compartments in the cell that normally break down toxic substances and recycle different types of molecules. Researchers propose that the CLN3 protein may help regulate the size and relative acidity (pH) of lysosomes.

How are changes in the CLN3 gene related to health conditions?

More than 60 mutations in the CLN3 gene have been identified in people with juvenile Batten disease. Juvenile Batten disease impairs mental and motor development beginning in childhood, causing difficulty with walking, speaking, and intellectual functioning. In addition, affected children often develop recurrent seizures (epilepsy) and vision impairment. The most common mutation that causes this condition deletes about 1,000 DNA building blocks (base pairs) in the CLN3 gene. This mutation, which is usually called the 1 kb deletion, removes a critical part of the gene. The 1 kb deletion disrupts the function of the CLN3 protein, leaving only a small amount of normal activity. It is estimated that more than 90 percent of individuals with juvenile Batten disease caused by CLN3 gene mutations have the 1 kb deletion.

Researchers are working to determine how mutations in the CLN3 gene lead to the characteristic features of juvenile Batten disease. These mutations somehow disrupt the function of lysosomes, resulting in the buildup of fatty substances called lipopigments in these cell structures. These accumulations occur in cells throughout the body, but neurons in the brain seem to be particularly vulnerable to the damage caused by lipopigments. The progressive death of cells, especially in the brain, leads to vision loss, seizures, and intellectual decline in people with juvenile Batten disease.

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